A variety of devices are available for separately monitoring intrauterine pressure and fetal heart rate of a pregnant mother and her fetus during pregnancy or labor. For example, to measure uterine contractions an external transducer diaphragm may be provided that is secured to the mother's abdomen by a belt or other device. During labor, contractions and/or intrauterine pressure may be sensed by the transducer diaphragm and displayed on a monitoring device. Such external devices, however, may be awkward to use, may slip and/or lose effective contact with the mother's abdomen, potentially resulting in less accurate uterine contraction information.
To monitor fetal heart rate, devices that are invasive to the fetus have been used to sense the fetal ECG from which the heart rate may be obtained. Such devices are generally positively fixed to the fetus, for example, by a harpoon tip or a corkscrew-type electrode, which are anchored or screwed into the scalp of the fetus. Alternatively, a suction cup device may be attached to the head of the fetus that includes a sensor therein. Such devices, however, generally require direct contact with the fetus, and often also require penetration of the fetus' skin, which may increase the risk of infection or other harm to the fetus.
More recently, devices have been developed which allow sensing of both pressure and fetal ECG in a single device. For example, U.S. Pat. No. 5,184,619 discloses a device having a pressure transducer and an array of electrodes spaced axially along the device for sensing fetal ECG. The device includes a tubular housing having a distal portion adapted for insertion into a woman's uterus and for placement adjacent to a fetus therein. Two or more electrodes are mounted along the distal portion spaced axially apart from one another, and a pressure transducer is also provided on the distal portion.
Preferably, the pressure transducer is a solid state differential pressure transducer with one side exposed for contacting fluid within the uterus. The other side of the pressure transducer is vented to atmosphere by a lumen extending to a proximal end of the housing. Cables from the electrodes also extend to the proximal end, where they may be connected to processor circuitry and/or a monitoring device which may display fetal ECG or heart rate.
Such devices generally include an external ground or reference electrode placed in contact with the mother's body, e.g., using a leg plate or an external ECG electrode. The reference electrode may facilitate the processor circuitry associated with the monitoring device in separating noise and other signals sensed by the electrode array from the fetal ECG signal. Even with the external reference electrode, the processor circuitry must perform complicated algorithms in order to obtain an accurate fetal ECG and/or fetal heart rate.
Accordingly, there is a need for an intrauterine pressure transducer, fetal ECG and/or fetal heart rate sensor that facilitates monitoring of a fetus, that is more convenient to use, and/or that is noninvasive to the fetus.